Due to layout and routing considerations in today's densely structured integrated circuits, it is sometimes required that a signal be routed from one location on an integrated-circuit die to another relatively distant location on the same die. Typically, this is accomplished by an electrical conductor that is routed between the two locations.
A problem with using an electrical conductor is that as the number of components in, and thus the size of, an integrated circuit increases to provide more functionality such as increased processing power and memory storage, the conductor often becomes longer, and thus the signal delay introduced by the conductor becomes greater. Therefore, the size of the integrated circuit may be restrained by the maximum delay that can be tolerated for such a routed signal, or additional circuitry may be needed to accommodate for the delay.
One technique for reducing the signal delay is to route the signals via an optical path or waveguide instead of an electrical conductor. For example, U.S. Pat. No. 5,485,021 discloses a semiconductor device that includes a transparent substrate, a thin semiconductor film disposed on the substrate, and circuitry formed in the thin film, where optical signals are routed through the transparent substrate. But a problem with the '021 technique is that there are many types of circuits and circuit components that are difficult or impractical to form in a thin film. Furthermore, the transparent substrate is a relatively lossy optical path. Therefore, an optical signal must have a power that is high enough overcome the losses introduced by the substrate. Because of the present trend towards reducing the power consumption of integrated circuits, having to generate such a relatively high-powered optical signal would often be undesirable.
Another example of an optical-routing technique is found in U.S. Pat. No. 5,604,835, which discloses optical waveguides that are disposed along the sidewalls of a substrate trench. But a problem with the '835 technique is that, because the waveguides are formed along the trench sidewalls, the trench must be relatively wide. Therefore, because circuitry can be disposed only in the substrate regions that are between the trenches, the area of the integrated circuit often must be increased by the relatively large area that the trenches occupy.